Preparation of color printing plates



June 15, 1943. w. MARTIN 2,321,760

PREPARATION OF COLOR PRINTING PLATES Filed Apnl 24, 1941 2 Sheets-Sheet 1 if [RE EM FAUNTF;

lNv ENT OR WczZier Mariz n Z TTORNEY June 15, 1943.,

w. MARTIN 2,321,760

PREPARATION OF COLOR PRINTING PLATES Filed April 24, 1941 2 Sheets-Sheet 2 REEN PAINT Fziy. 7.

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INVENTOR WaZz er- Martin BY (7 ATTORN Y and another.

Patented June 15, 1943 UNlTE sr'rss earner trio.

PREPARATION OF COLOR. PRINTING PLATES Walter Martin, Orange, N. J.

Application April 24, 1941, Serial No. 390,028

5 Claims.

My invention relates to a photo-engraving process or method and more particularly to a method of preparing plates for color printing.

to. insure that there shall be no gaps, or there would be a white streak between one color area In case of a slight inaccuracy in register, such a white streak or line between two color areas would be very noticeable, whereas a slight overlap would be relatively inconspicuous.

Heretofore in making the successive plates with the required overlap a negative was made from the original or copy and printed on a printing plate as, for example, a zinc plate. The areas of the plate on which the light acted through the. negative remained upon development and were covered with a resist; thereupon the plate was lightly etched and the resist removed so that the plate showed the picture or design in shaded and unshaded parts.

To prepare the plate for printing it was, therefore, necessary to rout out or cut away those portions of the plate which were not to be printed with a respective color and in doing so to leave a slight margin or overlap. g

Frequently the size of the plate is reduced from that of the copy and the detail is some What smaller which increases the difficulty of routing out or etching away undesired parts and to provide the necessary margin. Also the preparation of a plate by this method, as heretofore used, required considerable skill as well as carein] and tedious work.

In my invention I provide a method whereby the printing plate or negative for making such plates may be made with a suitable overlap directly by photographing from the original or Hc0py.!!

In my invention I outline each color on the copy with an outline, the thickness of the out-- duced the outline may be correspondingly thicker.

After eachcolor'area has thus been enclosed in the outline, the copy is covered with a transparent sheet of material, such as a prepared sheet of cellulose acetate, commonly known in the trade as acetate, so that the copy and the outline may be seen therethrough; then those color areas, enclosed by corresponding outlines, are filled in or painted black throughout the area, including the outline.

For example, if there is a green area enclosed in the outline, each such green area will be filled in with black up to or including the outline itself.

Other boundary lines not to appear are then painted white. The copy and superposed sheet thus preparedare then photographed onto a negative, whereupon the parts corresponding to the color, for example, green, appear transparent and the remaining portions black. The green area includes all of the copy that is green, plus the margin and is, therefore, slightly larger than the area corresponding to the color of the copy.

The process is repeated for each of the other colors to be printed as, for example, red. blue or yellow. Each of the negatives thus prepared may-be sent to the plate maker who may then prepare a printing plate from each negative thus supplied.

When these respective plates are used in print ing, each color will have a very slight overlap corresponding to the thickness of the margin.-

The method of my invention may be used with all types of printing now in use and alltypes of reproduction requiring line engraving.

The various features of the invention are illustrated in the accompanying drawings in which-- 7 Fig. 1 is a drawing of an original or copy from which a number of color printing-plates are to be made, having different colored areas outlined with a marginal line. Fig. 2 is a view similar to that of Fig. 1 in which the copy, is overlaid with a transparent sheet of acetate in which certain outline areas are being painted black, the outlines in remaining areas being painted in white. Fig. 3 is a view of a reduced negative made by photographing the copy and acetate sheet assembly of Fig. 2. Fig. 4 is a view similar to that of Fig. 2 showing a different area being blacked for a different color plate. Fig. 5 is a figure of a reduced negative made by photographing the copy and acetate sheet assembly of Fig. 4. Fig. 6 is a view of-a third acetate sheet superimposed on the copy and with the remaining areas forming the. background of the copy being blacked. Fig. 7 is a reduced negative of the copy and finished acetate sheet assembly of Fig. 6, and Fig. 8 is a greatly enlarged and foreshortened view of a reproduction printed in three colors namely, blue, red and green from plates made from-the negatives shown in Figs. 3, and 7, the part of the drawing at the right of the break showing the actually overlapping of the printed colors and the part at the left of the break showing the color boundaries as they actually appear in the finished print.

In the particular method shown in the accompanying drawings, a simple sign in three colors is illustrated, by way of example, it being understood that this illustration is chosen for its simplicity and that the invention may be applied to the printing of pictures and designs of more complicated outline than those shown in the drawings.

The sign shown in the drawings comprisesthe words Green paint printed in green on a blue background and with a border of red enclosing the printed portion. This is merely by way of example, it being understood that other color combinations may be employed.

In carrying on my invention and method, the words Green paint indicated at II! in the copy II and border I2 are outlined in substantial Black lines I3 and I4, the area within the lines I3 to be in green and the area within the lines Il to be in red and the remaining parts of the finished sign to be in-blue. The area entirely enclosed within the outlines is the area that is to be shown in green and red respectively.

After the copy has been outlined as illustrated in Fig. 1, it is covered by a transparent sheet I5 of acetate, or other suitable transparent material, so that the outlines show distinctly through the transparent sheet.

With the transparent sheet I5 fixed firmly in position the area Ill comprising the words Green paint is filled in by black paint. The painting of the area als overlaps the margin or outlines I3 and, therefore, covers all of the areas II] to the outer edges of the marginal or outline lines. This area is, therefore, somewhat greater than the areas ID by the thickness of the marginal or outline lines I'3'.

The parts of the acetate sheetoverlying the other outlines are painted white as indicated at I6. The result is a white background I6 on which the words Green-paint appear at I! somewhat thicker or larger than the size they are to have on the finished reproduction.

When the painting of the acetate sheet has thus been completed a negative is taken in which.

the part/I6 appears in black, as indicated at IT in Fig.3, and the parts that were painted black appear white, as indicated at I8.

It will be apparent that when a photo-sensitized plate is printed from this negative and developed, the parts corresponding to the white areas in the negative will be protected from the etching and the balance of the plate maybe etched away. This will leave a printing surface corresponding to the enlarged area of the blackened part of transparent sheet I5.

,After the above sheet I5 has been completed andphotographed another transparent sheet is prepared from which a negative for the red printing plate is made.

Inasmuch as the red area is to cover the space between the outlines I4 together with the thickness of the lines, a second transparent sheet I9 is placed on the copy and all of the area within the lines I4, and covering these lines, is painted black as indicated at 20, while the parts of the balance of the sheet overlying the other outlines are painted white as indicated at 2|.

From the sheet and copy assembly thus formed a negative is made of reduced scale to correspond to that of Fig. 3. In this negative the areas 20 will appear White, as indicated at 22, and the white areas 2| will appear black, as indicated at23. From this negative a plate suitable for printing a second color, as for example red, may be made.

To make a plate for printing the base color, blue in the example given, a third transparent sheet 24 is placed on the copy I I and the areas outside of the lines I3 and I4 are painted black as at 25 and 26, and this blacking of the transparent sheet is continued to the inner edges of the outline or marginal lines I3 and I4. Then the parts within these lines, corresponding to the red and green areas, as left uncovered so that they form white'areas. A reduced negative is then formed in which, as shown in Fig. '7, the white areas, which in the negatives of Figs. 3 and 5 appear white, are now black and the background parts are in white, as indicated at 21 and 28 respectively, so that'these parts will be protected in the etched plate and, therefore, form the blue printing surface.

It will be apparent from the above that the white areas of the negatives of Figs. 3 and 5 are slightly larger than the corresponding black parts of the negative of Fig. 7, the difierence corresponding to the thickness of theoutline lines I3 and I4, because in each case the black painting has included the particular color area together with the thickness of the respective lines.

Accordingly, when the respective printing plates are made and printed in the respective colors, there will be a slight overlap between the colors corresponding to the thicknesses of the marginal or outline lines I3 and I4. However, such an overlap will merely have the effect of slightly darkening the background about the lighter colors, if it has any noticeable effect whatsoever. It will insure, however, that there is no gap between the colors in the event that the registry of any two plates should not be perfect because such error in registry would have to exceed the thickness of the marginal or'outline lines I3 and I4, which willbe made sufiiciently wide to cover any permissible margin of error.

While the invention has been illustrated as applied to a simple line drawing, it will be understood that the printing s'urface made from the negatives may be of any suitable type as, for example, either a plain fiat surface, or a surface made by half-tone, Ben Day or other process. Also where a color is to be the result of the superimposing of two or more colors, the method of my invention may be employed in outlining the colors although certain areas will themselves overlap.

It will be apparent that by my. invention-it is only necessary to outline the different colored areas on the copy and that when this is done and the transparent sheet superimposed, the step of filling in the correct'areas is one that can be very easily and quickly made and without any exceptional skill but with only ordinary care. It is particularly advantageous where the copy is larger than the printing plates because the areas to be filled in are correspondingly larger and less care is required, inasmuch as any errors and inaccuracies are reduced in the photographic reduction in making the negatives.

It may be noted that the original or copy is not in color but is in black and white and may be a print or drawing, or photograph, etc. In some cases where there are not two adjoining colors the outlines are merely color boundary lines.

What I claim is:

1. A method in the preparation of negatives for photo-printing in color which comprises outlining with boundary lines the respective color areas in an original to be reproduced, covering said outlined original with successive transparent sheets, one for each plate to be made, blacking the areas of said transparent sheet within said boundary lines corresponding to the selected color of said sheet and photographing negatives from assemblies of said transparent sheets and copy to reproduce transparent areas corresponding to the black area of said transparent sheet and copy including the width of said margin lines.

2. A method in the preparation of negatives for photo-printing in color which comprises outlining the respective color areas in an original to be reproduced, covering said original with successive transparent sheets, one for each plate to be made, blacking the area of each transparent sheet within said boundary line enclosing the corresponding color area and photographing a reduced negative from said transparent sheet and copy to reproduce transparent areas corresponding to the blacked area of the transparent sheet and copy including the width of the margin lines.

3. A method in the preparation of negatives for photo-printing in color which comprises outlining with boundary lines the respective color areas in an original to be reproduced, covering said original with successive transparent sheets, one: for each plate to be made, blacking the areas of'said transparent sheets within the boundary lines of the areas corresponding to the respective colors to be reproduced, painting over the outlines in the remaining areas in white and photographing a negative from each assembly of transparent sheet and original to reproduce transparent areas corresponding to the black area of said transparent sheet and original including the: Width of said margin lines.

4, A method of providing an overlap of negatives for reproducing color printing plates which comprises drawing a boundary line of a width corresponding to said overlap between contacting color areas on an original to be reproduced, covering said original with a transparent sheet, blacking said sheet over one of said color areas to said boundary line and photographing a negative of said assembly of original and blackened sheet to reproduce transparent areas corresponding to said blacked area and boundary line.

5. A method of providing an overlap of negatives for reproducing color printing plates which comprises drawing a boundary line between contacting color areas of an original to be reproduced, covering said original with a transparent sheet, blacking said transparent sheet to and including said boundary line while painting over the boundary lines in the remaining areas in white and photographing a negative from said transparent sheet and original to reproduce transparent areas corresponding to the black area of said transparent sheet and original including th width of said margin lines.

WALTER MARTIN. 

